Currently marketed heavy-duty vehicle tyres have a tendency to pick up road surface debris (typically stones), which clings, even for long periods of time, to the inside of the longitudinal (circumferential) tread grooves. As the tyre rolls along the road surface, the debris clinging to the longitudinal grooves in the tread is rammed cyclically to the bottom of the grooves, thus damaging the rubber (in the worst case scenario, the debris may even be elongated, with a pointed tip facing the bottom of the groove). In addition, debris retention inside the longitudinal tread grooves forms ‘dams’, which prevent water from running off and draining along the grooves, thus impairing wet-pavement road-holding performance of the tyre.
Debris retention inside the longitudinal tread grooves is especially problematic in the case of winter tyres, which have at least one zigzag-shaped longitudinal groove—i.e. each sidewall of the longitudinal groove has a continuous sequence of alternating transverse (axial) projections and recesses —designed to trap snow (and so improve road-holding performance on snow-covered roads), but which also forms a succession of longitudinal debris-retaining ‘pockets’.
Patent application JP2008296795 discloses a pneumatic tire reducing stone trapping in a main groove. In the pneumatic tire, a central main groove and a shoulder main groove are provided on a tread part; in the central main groove and the shoulder main groove, a groove wall surface in a groove cross section perpendicular to a groove length direction comprises a base part vertically extending from a groove bottom to a tread stepping surface side or extending at an inclination in a direction for increasing groove width and a slack slope part extending from an upper end of the base part to a tread stepping surface at the slack inclination than the base part.